Acoustic pick-up

ABSTRACT

An acoustic pick-up, particularly an ultrasonic pick-up for acoustically diagnosing machines, for example, for detecting leakage in valves or for diagnosing positions, comprising a piezoelectric measuring element and an electronic circuit that processes the measurement signal into a form that is suited for transmission to an evaluation device. In order that the acoustic pick-up can function without an external auxiliary power supply, means are provided by means of which auxiliary power required for operating the electronic circuit can be generated from the acoustic signal to be picked up.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/005826, filed May 28, 2004 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10325801.9 DE filed Jun. 6, 2003, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to an acoustic pick-up, more particularly anultrasonic pick-up for acoustically diagnosing machines.

BACKGROUND OF INVENTION

In many areas of process and power engineering that are of relevance tosafety the trouble-free operation of a system depends on the smoothfunctioning of the machines or machine parts employed. In order to avoidcostly, erratic interruptions to operation, any damage to valves orbearings, for instance, should as far as possible be detected at theinitial stage, which is to say before a component outage can bring thesystem to a halt. As an instance of this, defective valve seats willresult in leakage flows that produce broadband ultrasonic emissions.Picking up and evaluating the ultrasonic emissions of a valve can henceserve to detect valve damage early. An ultrasonic pick-up suitable forpicking up the solid-borne sound signal is known from DE 299 12 847 U 1.Said pick-up has a housing containing a piezoelectric measuring elementand a circuit for signal conditioning. The conditioned measurementsignal can be ducted as an output signal over a cable to a remotelylocated evaluation device. The auxiliary power required to operate thesignal conditioning circuit is supplied by the evaluation device andmade available to the acoustic pick-up likewise via the cable. Thismeans an additional device for generating the auxiliary power isrequired in the evaluation device and additional wires for transmittingsaid auxiliary power are required in the cable.

A monitoring sensor using wireless signal transmission (wirelesstransducer) is known from EP 1 022 702 A2, which wireless transducerhas, mounted within a housing, a piezoelectric sensing element forgenerating an electric monitoring signal and an electronic circuit.

The auxiliary energy required to operate the electronic circuit and forsignal transmission is obtained from the electric monitoring signal.

A further monitoring system using wireless signal transmission is knownfrom U.S. Pat. No. 4,237,454.

SUMMARY OF INVENTION

An object of the invention is to provide an acoustic pick-up, moreparticularly an ultrasonic pick-up for acoustically diagnosing machines,which pick-up can function without an external auxiliary power supplyand enables a measurement signal to be transmitted in a frequency rangethat is to be evaluated.

To achieve said object the new acoustic pick-up of the type mentioned atthe start has the features described in the claims.

The invention has the advantage that the acoustic pick-up takes thepower needed to operate an electronic circuit for signal conditioningfrom its surroundings so that said power does not have to be supplied toit over separate wires in a cable. As the acoustic pick-up generates theauxiliary power from the acoustic signal requiring to be picked up,sufficient power will always be available for operating the circuit attimes when an acoustic signal exceeding a specific minimum intensity ispresent and a corresponding output signal has to be produced. The outputsignal can be transmitted to the evaluation device asymmetrically orsymmetrically over a cable, for example, or alternatively wirelesslyusing radio or infrared light.

The auxiliary power is generated from the electric measurement signal ofthe piezoelectric measuring element. This has the advantage that nofurther electroacoustic components will be required in addition to theactual measuring element of the acoustic pick-up.

When acoustic pick-ups are used for machine diagnosing, in particularfor diagnosing valve leakage or damage to a bearing, evaluating aspecific frequency range has proved in most cases adequate for obtaininga diagnostic result. It is known from, for instance, DE 199 47 129 A1how when valve leakage is being diagnosed to distinguish between a lowerspectral range in which mainly the valve's operating noises are locatedand an upper spectral range predominantly containing fault-generatednoises in certain operating conditions. The threshold frequency betweensaid two spectral ranges can be selected to be between 50 kHz and, forexample, 200 kHz since the operating noises occur predominantly in arange below 120 kHz. A spectral range of the measurement signal above afrequency of 50 kHz is therefore evaluated for detecting faults, whichrange does not, however, have to begin directly at 50 kHz. Only signalcomponents in that frequency range have to be amplified and transmittedon a wire-bound basis or wirelessly to the evaluation device. The signalsupplied by the piezoelectric measuring element is especially powerfulin the frequency range between 0 and 50 kHz because the signalcomponents have a substantially greater amplitude therein. The signalcomponents in that range can advantageously be used for generating thepower required for operating the conditioning circuit. There is thusadvantageously provided a frequency separating filter by means of whichthe electric measurement signal of the piezoelectric element isseparated essentially into an evaluation signal in a first frequencyrange, which signal is conditioned into a form suitable for transmittingto an evaluation device located outside the housing, and into a supplysignal in a second frequency range, which signal supplies the auxiliarypower required for operating the conditioning circuit. A frequencyseparating filter of said type furthermore offers the advantage that theevaluation signal will be falsified only slightly despite the supplysignal being derived from the same electric measurement signal.

A better quality for the auxiliary power for the circuit for signalconditioning and hence a better quality for the output signal willadvantageously be achieved if a device for rectifying and smoothing thesupply signal is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as well as embodiments and advantages are explained inmore detail below with the aid of the drawings illustrating an exemplaryembodiment of the invention:

FIG. 1 is a partial cross-sectional view of an acoustic pick-up and

FIG. 2 is a block diagram of the electronic components of said acousticpick-up.

DETAILED DESCRIPTION OF INVENTION

Shown in the bottom half of FIG. 1, which is to say below an axis 1, isa side view of an essentially rotationally symmetrically structuredacoustic pick-up, and in the top half a longitudinal section throughsaid acoustic pick-up.

According to FIG. 1 the acoustic pick-up has a pot-shaped housing 2furnished on its exterior with driving flats 3 for a wrench. Provided asa securing means is a threaded stem 4 that can be turned into acorresponding threaded boring at the mounting position. The requisitestarting torque can be applied by means of a wrench to ensure goodcoupling of the vibrations via a contact surface 5 of the housing baseat the mounting position. Inside the housing base is an insulating disk6 of the same material as that also of a piezoelectric element 7 ontowhich has been soldered a metal-plated side of said insulating disk 6,which side faces a sleeve section 8. Together with a sleeve section 9and a disk spring 10, said 10, said sleeve section 8 forms a sleeveextending along the entire length of the acoustic pick-up's measuringelectronics and constituting a major part of the electromagneticshielding. Connecting leads 11 and 12 for electrically connecting asignal electrode 13 or, as the case may be, measuring electrode 14 ofthe piezoelectric measuring element 7 to an electronic circuit 15, theelectronic circuit 15 itself, and electric supply leads 16 to theelectronic circuit are furthermore shielded within the sleeve fromelectromagnetic interference. The electronic circuit 15 serves toconvert the charge transfers in the piezoelectric measuring element 7due to acoustic vibrations into a signal that can be transmitted welleven over longer distances via a cable or, as an alternative to theexemplary embodiment shown, wirelessly. One basal area of the sleeve issealed by the electrically conducting metal coating of the insulatingdisk 6. Said metal coating serves simultaneously as a measuringelectrode 14. Within the other basal area the sleeve's inner wall isfurnished with an internal thread into which a BNC jack 17 has beenturned until a circumferential collar 18 of said BNC jack 17 comes torest against a seal 19. Other types of plug connectors can, of course,also be used as alternatives to the BNC jack, or the cable can beconnected directly in the sleeve. The sleeve is secured in position by asealing part 20 which at least partially overreaches the sleeve's otherbasal area and is furnished with an internal thread which has beenturned as far as the stop 21 onto a corresponding external thread of thehousing 2. Located between the sleeve's end face and the inner wall ofthe housing 2 is an insulating foil 22. Reference is made to DE 299 12847 U1 for further details of the acoustic pick-up's structural design.

According to FIG. 2 an acoustic pick-up picks up an acoustic signal bymeans of a piezoelectric measuring element 30 that convertsstructure-borne sound into an electric measurement signal 31 over a widefrequency range. Said measurement signal 31 is ducted to a frequencyseparating filter 32 consisting essentially of a first filter 33 and asecond filter 34. The first filter 33 is permeable for the signalcomponents of the electric measurement signal 31 that are above athreshold frequency of 50 kHz. An evaluation signal 36 will thereforecontain nothing but higher-frequency components, which in the exemplaryembodiment shown are evaluated for diagnosing leaks. When an outputsignal 40 is transmitted over a cable to a remotely located evaluationdevice (not shown in the drawing), an amplifier 41 serves to conditionthe evaluation signal 36 into a form suitable for transmission. Forwireless transmission, as an alternative to the exemplary embodimentshown it would be possible additionally to provide an HF modulator andan antenna for generating a corresponding radio signal as the outputsignal in the conditioning circuit 35. The second filter 34 is permeablefor the signal components of the electric measurement signal 31 that arebelow a threshold frequency of 50 kHz and, although having a largeamplitude, are of secondary importance for obtaining a diagnosticresult. A supply signal 37 passing through the filter 34 is rectifiedand smoothed in a device 42. A smoothed supply signal 43 is thusavailable for the amplifier 41 so that good quality can be ensured forthe output signal 40. The filters 33 and 34, the amplifier 41, and thedevice 42 are hence constituent parts of the electronic circuit whichconditions the electric measurement signal 31 into a form suitable fortransmitting to an evaluation device located outside the acousticpick-up housing and which thereby advantageously functions without anexternal auxiliary power supply.

As an alternative to the exemplary embodiment shown, for generating asupply signal it is of course possible to provide a furtherelectroacoustic transducer which from the acoustic signal requiring tobe picked up supplies a powerful electric signal from which can begenerated the auxiliary power for a circuit for conditioning themeasurement signal. An additional transducer of said type can, however,be advantageously omitted from the exemplary embodiment described.

1-4. (canceled)
 5. An ultrasonic pick-up for acoustically diagnosingmachines, comprising: a piezoelectric measuring element for generatingan electric measurement signal; a housing that includes thepiezoelectric measuring element; an auxiliary power generated from theelectric measurement signal; a electronic circuit operatively connectedto the piezoelectric measuring element, the electronic circuit adaptedto convert the electric measurement signal to a form suitable fortransmission to an evaluation device located outside of the housing; anda frequency separating filter for separating the electric measurementsignal into: an evaluation signal in a first frequency range, and asupply signal in a second frequency range.
 6. The ultrasonic pick-upaccording to claim 5, further comprising a rectifying device forrectifying and smoothing the supply signal.